Work is in progress to purify human amidophosphoribosyltransferase and study the physical and kinetic properties of this enzyme. Purification has been completed and the protein demonstrated to contain iron and sulfide. Work is also in progress to characterize the kinetic properties of a mutant form of amidophosphoribosyltranferase which has been isolated from a mammalian cell culture line. The mutant enzyme has an altered affinity for glutamine. In addition, studies are being conducted to evaluate whether changes in purine nucleotide content of myocardium and skeletal muscle are responsible for the muscle dysfunction observed in ischemic heart disease and in the inherited myopathy of AMP deaminase deficiency.